1. Field of the Invention
The present application relates generally to anti-rotation devices used to prevent wear in the rotating control systems of helicopters and tilt rotor aircraft and, more particularly, to a method and apparatus for limiting the rotation of an actuator rod used to manipulate the non-rotating swashplate of a swashplate system.
2. Description of Related Art
Tilt rotor aircraft are hybrids between traditional helicopters and traditional propeller driven aircraft. Typical tilt rotor aircraft have fixed wings that terminate with convertible tilt rotor assemblies that house the engines and transmissions that drive the rotors. Tilt rotor aircraft are convertible from a helicopter mode, in which the tilt rotor aircraft can take-off, hover, and land like a helicopter; to an airplane mode, in which the tilt rotor aircraft can fly forward like a fixed-wing aircraft.
Helicopters and tilt rotor aircraft use rotating control systems. A rotating control system typically consists of a rotating swashplate and a non-rotating swashplate connected by a bearing system. The rotating swashplate tracks the movements of the non-rotating swashplate, and the angle of the main rotor blades are adjusted accordingly. The non-rotating swashplate is manipulated by the pilot by way of hydraulic actuators. Each actuator rod is attached to one of several clevises of the non-rotating swashplate at a spherical bearing. The spherical bearing is held in place by a bearing housing at the end of the actuator rod.
The spherical bearing permits rotational misalignment of the actuator in all axes. The misalignment of the spherical bearing is determined and controlled by inputs from the flight control system. Rotation of the actuator about its own longitudinal axis is not restricted, nor can it be limited or controlled by inputs from the flight control system. Because of this condition, the bearing housing is able to rotate within the clevis such that it comes into contact with an inner surface of the clevis. Such contact causes wear resulting in structural damage to both the clevis arms and the bearing housing. Since the clevis arms are integral to the non-rotating swashplate, damage to the clevis arms compromises the structural integrity of the non-rotating swashplate. Damage to the non-rotating swashplate causes a hazardous condition that could cause a pilot to loose control of the helicopter or aircraft. Devices have been inserted into the clevis to limit excessive rotation of the actuator. Such devices have caused premature wear and damage to the bearing housings from the introduction of debris, thereby compromising the structural integrity of the actuator.
Due to the flight-critical nature of the non-rotating swashplate and actuator, there has been a desire to minimize wear and damage to the clevis arms and bearing housing. The solution to the problem in the past has been to install wear pads between the bearing housing and the clevis arms. This approach does protect the clevis but does not protect the bearing housing, which is worn because of contact with the pads. An additional problem is that the wear pads may require frequent replacement, resulting in added costs and aircraft down time.
Although great strides have been made in anti-rotation devices, considerable shortcomings remain.
While the system and method of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the application to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the process of the present application as defined by the appended claims.